1. Field of the Invention
The present invention relates to a lead acid battery, particularly to a sealed lead acid battery with an electric circuit having at a part thereof a protector for protecting the battery from short circuit or unusual generation of heat, which is generally called a thermal protector or thermostat, and more particularly to an improvement of the structure of the protector by which the protector is mounted onto a terminal box for containing the protector.
2. Description of Related Art
In lead acid batteries with a plurality of cell chambers containing a group of electrode plates or cell elements, the cell chambers are arranged either in one direction or in a U-shaped manner. However, in many cases where batteries have an elongated appearance, the cell chambers are primarily arranged in a row in one direction and connected in series to each other.
Sealed lead acid batteries of a small size with cell chambers arranged in a row have been increasingly required to be light and so handy that they can be mounted in a one touch onto an appliance. In response to this requirement, a manner is taken in which a pair of input and output terminals of a battery are contained in a terminal box provided on one end of an elongated container of the battery.
This manner is such that one of the positive and negative terminals in the terminal box is connected to one of the positive and negative terminals provided on the cell element in the cell most distant from the terminal box, through a lead provided across the opening of the container. The terminal box has a pair of windows exposing a pair of charging and discharging terminals. A pair of input and output terminals are provided on a frame-shaped electrically insulating terminal holder at the right and left ends thereof. The terminal holder is provided at the back side thereof with a recess. A thermostat as a protector is mounted in the recess. The thus formed terminal holder is inserted into the terminal box, and the electric connection is made in the manner as mentioned above, thereby obtaining the battery. The thermostat is provided with such a structure that it is brought into contact with a partition wall separating the cell chamber and the terminal box to raise the heat sensitivity thereof.
Such conventional structure gives a good operation in mounting the pair of input and output terminals and the thermostat onto the terminal holder and then inserting the holder into the terminal box. However, contact between the thermostat and the partition wall is often made poor in the conventional structure, due to unstable mating between the terminal holder or unstable mating between the terminal holder and the terminal box.
This poor contact between the thermostat and the partition wall provides so insufficient heat conduction from the partition wall to the thermostat that adequate heat sensitivity is not given. In the worst case, the battery container may be thermally deformed. That is, when the battery is overcharged, the cell element in the cell chamber may generate heat, which transfers through the partition wall at the bottom of the cell chamber to the thermostat. Overheating due to this overcharge is prevented by switching the thermostat from "on" to "off" to break the circuit. Therefore, the contact between the partition wall and the thermostat adjacent to the wall or the state of heat conduction is an important factor.